Revert 226823 "Refactored loading of applications" because it introduced a data race.

BUG=304180


> Refactored loading of applications / extensions icons.
> Added ImageLoader::LoadExtensionIconAsync() and ImageLoader::LoadExtensionIconDataURLAsync().
> Moved all apps / extension loading code to ImageLoader.
> 
> BUG=297298,297301
> 
> Review URL: https://codereview.chromium.org/25050005

TBR=dvh@chromium.org

Review URL: https://codereview.chromium.org/25996004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227003 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227003